No advice to give here except to say my depression really only sucks after mania. I live through mild depression myself - things I think are normal score on the beck depression inventory as mildly depressed nearly or just subthreshold. What I will say and I almost posted this in response to I think apfei's post about self-control:

For my personality, at least, which is not everyone's - seeing myself accomplish something makes me want to accomplish more. I don't feel in retrospect that I am more able to do things when manic. I do feel more unable to do things when depressed. I think that manic 'can do' feeling is fleeting/misleading compared to real motivation and drive. What helps me when I can't accomplish things or think I can't accomplish things is just to make things simple enough that I can see measurable progress. Seeing that progress improves my mood and makes me able to do more. During my last black depression (which came after my last manic episode), what pulled me out was this app called 'trello' where you can make todo lists and check things off. My brain said "this is too much" and "I can't do anything! I'm useless!" but I just slowly started checking things off, even when my black depression hadn't lifted, I had still done that one thing. I see no purpose (but still do it) in indulging "I can't do anything" when feeling depressed. It's counterproductive. Even if I start the day sad, I just do something. I have found it easier and easier to work past the low feelings the more they do come as you mention - you know that it's going to happen, so it's not something to be scared of. Just expect it will pass at some pt.

Anyway, maybe useless advice because I do not any longer believe that mania helps me get anything done so my experience of bipolar may be different than most.